Sustained Gamma-Ray Emission Events at the Sun

 

Pertti A. Makela
Research Associate - Solar Physics Laboratory
NASA Goddard Space Flight Center
Institute for Astrophysics and Computational Sciences (IACS)
The Catholic University of America 

Wed, November 1, 2023 - 4:00 PM

Sustained gamma-ray emission (SGRE) events differ from typical gamma-ray flares at the Sun by having a prolonged second phase of >100 MeV gamma-ray emission lasting up to several hours after the impulsive phase of the flare. Observations by the Large Area Telescope on board the Fermi satellite have shown that SGRE events are relatively common. SGREs are produced by >300 MeV protons interacting with plasma particles in the solar atmosphere and creating neutral pions, which decay into gamma rays. The source of these high-energy protons is still debated. Suggested sources include both flares and shocks driven by coronal mass ejections (CMEs). In this presentation we will discuss observational evidence supporting the idea that the >300 MeV protons travel back to the solar atmosphere from the CME-driven shock located tens of solar radii from the Sun and produce the neutral pions responsible for SGRE. Our recent discovery that the durations of decameter-hectometric type II radio bursts and the SGRE durations are linearly correlated provides clear suppport for a CME-shock as the particle source. In addition, the properties of SGRE-associated CMEs resemble those of CMEs producing ground level enhancements (GLEs). GLEs are large particle events detected by neutron monitors on the ground when high fluxes of solar protons with energies of several hundreds of MeV interact with Earth's atmosphere after a major eruption at the Sun.

Refreshments served at 3:45 PM

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